1. Field of the Invention
The invention generally relates to an optical apparatus, and more particularly, to a projection apparatus.
2. Description of Related Art
A projection apparatus is a display apparatus for producing large-size frames. The imaging principle of the projection apparatus is based on converting an illumination beam produced by a light source into an image beam through a light valve, followed by projecting the image beam through lenses onto a screen or a wall to form images. Along with the progress of projection technology and reduction of manufacturing cost thereof, the application of the projection apparatus has been gradually expanded to home purpose from commercial purpose.
A variation of light source luminance or an ambient temperature variation may cause the lenses, the beam-deflecting component used in association with the lenses or other structures in a projection apparatus to have thermal expansion and contraction phenomena, which further leads to a displacement of the focal point of the lenses and accordingly affects projection frames. For example, after turning on a projection apparatus, the temperature therein would gradually rise. At the time, the lenses, the beam-deflecting component or other structures get thermal expansions so that the lenses are unable to precisely focus the light beam at a light valve and thereby, the projection frames gradually become faint, so that a user needs re-focusing to resume normal projection frames. Such re-focusing makes the operation inconvenient and affects the projection quality.
Taiwan Patent No. 1229757 discloses a lens assembly used in projection TV set where a thermal expansion of a structure is utilized to compensate thermal twisting or other optical property variations of the lens components affected by heat. In addition, Taiwan Patent Application Publication No. 200848779 discloses a lens module where a hot bending of a compensation piece is utilized to make a lens barrel move so as to keep the imaging plane of the lens module locating at a predetermined plane.